Sensing devices

ABSTRACT

A sensing device includes a first sensor configured to capture a first analyte in a fluid medium and to generate a first signal in response to capturing the first analyte. The sensing device also includes a second sensor configured to capture a second analyte in the fluid medium and to generate a second signal in response to capturing the second analyte, where the second analyte is different from the first analyte. The sensing device further includes a detector configured to collect the first and second signals to provide a total signal and to calculate a total concentration of the first and the second analyte in the fluid medium based on the total signal.

TECHNICAL FIELD

The present disclosure relates to sensing devices, for example, asensing device configured to sense analytes in an aqueous solution.

BACKGROUND

Calcium (Ca) and magnesium (Mg) ions are generally responsible for thehardness of water. Elevated levels of Ca²⁺ and Mg²⁺ ions in water affectthe performance and maintenance of appliances contacting the water.Efficiently detecting and monitoring a total hardness of water may bebeneficial to a user, such as helping the user maintain water qualityand improve the performance of appliances.

SUMMARY

According to one embodiment, a sensing device is disclosed. The sensingdevice may include a first sensor configured to capture a first analytein a fluid medium and to generate a first signal in response tocapturing the first analyte. The sensing device may further include asecond sensor configured to capture a second analyte in the fluid mediumand to generate a second signal in response to capturing the secondanalyte. The second analyte is different from the first analyte. Thesensing device may also include a detector configured to collect thefirst and the second signal to provide a total signal and to calculate atotal concentration of the first and the second analyte in the fluidmedium based on the total signal.

According to another embodiment, a sensing device is disclosed. Thesensing device may include a sensor film including a mixture of sensors.The mixture of sensors may include first and second sensors. The firstand second sensors may be mixed by a mixing ratio. Each of the first andsecond sensors may be configured to capture an analyte in a fluid mediumhaving at least one analyte and to generate a signal in response tocapturing the analyte. The sensing device may further include a detectorconfigured to collect signals from each of the first and second sensorsupon each of the first and second sensors capturing one of the at leastone analyte in the fluid medium to provide a total signal and tocalculate a total concentration of the at least one analyte in the fluidmedium based on the total signal.

According to yet another embodiment, a sensing device is disclosed. Thesensing device may include a sensor film including a mixture of sensors.The mixture of sensors may include first and second sensors. The firstand second sensors may be mixed by a mixing ratio. Each of the first andsecond sensors may be configured to capture an analyte in a fluid mediumand to generate a signal in response to capturing the analyte. Thesensing device may further include a first detector configured tocollect a first signal having a first frequency from at least one of thefirst and second sensors in the sensor film upon the at least one of thefirst and second sensors capturing a first analyte in the fluid mediumand to calculate a first total concentration of the first analyte in thefluid medium based on the first signal. The sensing device may alsoinclude a second detector configured to collect a second signal having asecond frequency from at least another one of the first and secondsensors in the sensor film upon the at least another one of the firstand second sensors capturing a second analyte in the fluid medium and tocalculate a second total concentration of the second analyte in thefluid medium based on the second signal. The second frequency isdifferent from the first frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a schematic diagram of a sensing device according to thepresent disclosure.

FIG. 2 depicts a schematic diagram of a chemosensor configured to beused in the sensing system described in FIG. 1 .

FIG. 3 depicts a schematic diagram of another sensing device accordingto the present disclosure.

FIG. 4 depicts a graph including three titration curves of signal/s₀ asa function of the concentration of the analyte A (c₁) for threedifferent dissociation constants.

FIG. 5 depicts a graph of titration curves of signal/s₀ as a function ofthe total hardness of water (dGH).

FIG. 6 depicts a schematic diagram of yet another sensing deviceaccording to the present disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to beunderstood, however, that the disclosed embodiments are merely examplesand other embodiments can take various and alternative forms. Thefigures are not necessarily to scale; some features could be exaggeratedor minimized to show details of components. Therefore, specificstructural and functional details disclosed herein are not to beinterpreted as limiting, but merely as a representative basis forteaching one skilled in the art to variously employ the embodiments. Asthose of ordinary skill in the art will understand, various featuresillustrated and described with reference to any one of the figures canbe combined with features illustrated in one or more other figures toproduce embodiments that are not explicitly illustrated or described.The combinations of features illustrated provide representativeembodiments for typical applications. Various combinations andmodifications of the features consistent with the teachings of thisdisclosure, however, could be desired for applications orimplementations.

This present disclosure is not limited to the specific embodiments andmethods described below, as specific components and/or conditions may,of course, vary. Furthermore, the terminology used herein is used onlyfor the purpose of describing embodiments of the present disclosure andis not intended to be limiting in any way.

As used in the specification and the appended claims, the singular form“a,” “an,” and “the” comprise plural referents unless the contextclearly indicates otherwise. For example, reference to a component inthe singular is intended to comprise a plurality of components.

The description of a group or class of materials as suitable for a givenpurpose in connection with one or more embodiments implies that mixturesof any two or more of the members of the group or class are suitable.Description of constituents in chemical terms refers to the constituentsat the time of addition to any combination specified in the descriptionand does not necessarily preclude chemical interactions amongconstituents of the mixture once mixed.

Except where expressly indicated, all numerical quantities in thisdescription indicating dimensions or material properties are to beunderstood as modified by the word “about” in describing the broadestscope of the present disclosure.

The first definition of an acronym or other abbreviation applies to allsubsequent uses herein of the same abbreviation and applies mutatismutandis to normal grammatical variations of the initially definedabbreviation. Unless expressly stated to the contrary, measurement of aproperty is determined by the same technique as previously or laterreferenced for the same property.

The term “substantially” may be used herein to describe disclosed orclaimed embodiments. The term “substantially” may modify any value orrelative characteristic disclosed or claimed in the present disclosure.“Substantially” may signify that the value or relative characteristic itmodifies is within ±0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5% or 10% of thevalue or relative characteristic.

Reference is being made in detail to compositions, embodiments, andmethods of embodiments known to the inventors. However, it should beunderstood that disclosed embodiments are merely exemplary of thepresent disclosure which may be embodied in various and alternativeforms. Therefore, specific details disclosed herein are not to beinterpreted as limiting, rather merely as representative bases forteaching one skilled in the art to variously employ the presentdisclosure.

Hard water typically contains cations, such as calcium ions (Ca²⁺) andmagnesium ions (Mg²⁺), which can form deposits, such as calciumcarbonate (CaCO₃), in water. Such deposits may form more easily in a hotwater system, such as a heat exchanger or a steam oven, where Ca²⁺ andMg²⁺ ions may react with carbon dioxide at high temperatures to generatethe deposits. Because the deposits are thermally insulating, theformation of the deposits adversely affect thermal flows, leading topoor heat transfer in the hot water system.

The total hardness of water is the measurement of the concentration ofdivalent ions (e.g. Ca²⁺ and Mg²⁺ ions) in the water, typicallyexpressed as milligrams per liter (mg/L) or parts per million (ppm) ofCaCO₃. The total hardness of water can also be referred to as “degreesof general hardness” (dGH), or “degrees of German hardness”, where 1 dGHcorresponds to 17.848 ppm CaCO₃.

Ion sensing is applicable to the determination of the total hardness ofwater. For example, fluorescence-based detection methods have beenutilized to sense ions (e.g. metal ions) in water, where an ion binds toa detecting molecule to either generate or quench fluorescence.Measurement of the fluorescence can subsequently determine theconcentration of the ion in the water. However, because different ionshave different sizes and require different binding energies when bindingto different detecting molecules, the conventional fluorescence-baseddetection methods may thus exhibit different sensitivities toward thesensing of different ions. Moreover, these methods may only detect onetype of ion at a time.

Apart from the fluorescence-based detection methods, water-solublesensors have also been employed to detect ions in water. However,because the sensors can dissolve in water, this unavoidably bringscontaminates into the water, and the sensors are not reusable.Therefore, there is a need to detect ions in an aqueous environment in amore efficient manner.

Aspects of the present disclosure relate to a sensing device that maydetect at least one type of analyte in a fluid medium (e.g. water) andthat may be used to determine a total hardness and/or a total toxicityof the fluid medium. In one embodiment, the present disclosure relatesto a sensing device including two sensors, where each of the two sensorsmay be configured to detect an analyte in the fluid medium. In anotherembodiment, the present disclosure relates to a sensing device includinga sensor film, where the sensor film further includes a mixture ofsensors by a mixing ratio α. In yet another embodiment, the presentdisclosure relates to a sensing device including a sensor film embeddedwith a mixture of sensors by a mixing ratio α, and two detectors, whereeach of the two detectors may be configured to detect signals ofspecific frequencies.

FIG. 1 depicts a schematic diagram of a sensing device according to thepresent disclosure. The sensing device 10 includes an inlet 12, anoutlet 14, a first sensor 16 configured to detect a first analyte in afluid medium (e.g. water), a second sensor 18 configured to detect asecond analyte different from the first analyte in the fluid medium, anda detector 20. The detector 20 may be a photodetector. In oneembodiment, the first sensor 16 may be a chemosensor with a firstreceptor configured to coordinate to the first analyte. Uponcoordination by the first analyte, the first sensor 16 may generate afirst signal (e.g. fluorescence). Similarly, the second sensor 18 mayalso be a chemosensor with a second receptor configured to coordinate tothe second analyte. Upon coordination by the second analyte, the secondsensor 18 may generate a second signal (e.g. fluorescence). The detector20 may combine the first and second signals to calculate a total signal.Further, the detector 20 may be configured to determine a totalconcentration of the first and second analytes in the fluid medium basedon the total signal.

Apart from chemosensors, the sensing device 10 may also incorporateother types of sensors for analyte detection. Moreover, the sensingdevice 10 may include more than two sensors such that the sensing device10 may detect multiple analytes at one time.

In one embodiment, the sensing device 10 may be employed to determine atotal hardness of water. As discussed above, Ca²⁺ and Mg²⁺ ionscontribute mostly to the total hardness of water. Therefore, in thisembodiment, the first sensor 16 may be a chemosensor with a firstreceptor configured to coordinate to Ca²⁺ ions in the water, and thesecond sensor 18 may be a chemosensor with a second receptor configuredto coordinate to Mg²⁺ ions in the water. After water enters the sensingdevice 10 via the inlet 12, Ca²⁺ ions in the water may bind to the firstreceptor of the first sensor 16, generating a first signal (e.g.fluorescence). On the other hand, Mg²⁺ ions in the water may bind to thesecond receptor of the second sensor 18, generating a second signal(e.g. fluorescence). The detector 20 may gather the first and secondsignals to obtain a combined signal, which may be subsequently used tocalculate a total concentration of the Ca²⁺ and Mg²⁺ ions in the water.

The total hardness of water is substantially proportional to the totalconcentration of the Ca²⁺ and Mg²⁺ ions in the water. A general formulafor calculating the total hardness of water (dGH) is expressed as shownbelow as formula (1):f(c _(Cα) ,c _(Mg))=dGH=5.608(c _(Cα) +c _(Mg))  (1)In formula (1), c_(Ca) represents the concentration of Ca²⁺ ions in thewater, and c_(Mg) represents the concentration of Mg²⁺ ions in thewater, both in units of mmol/L. Therefore, based on a totalconcentration of the Ca²⁺ and Mg²⁺ ions in the water, the total hardnessof the water can be calculated according to formula (1).

In another embodiment, the sensing device 10 may be used to analyze atotal toxicity of water. The total toxicity of water may be due to thepresence of heavy metal ions in water, such as lead ions (Pb²⁺), mercuryions (Hg²⁺), cadmium ions (Cd²⁺), or arsenic ions (As³⁺ or As⁵⁺).Therefore, in this embodiment, the first sensor 16 may be a chemosensorwith a first receptor configured to coordinate to Pb²⁺ ions in thewater, and the second sensor 18 may be a chemosensor with a secondreceptor configured to coordinate to Hg²⁺ ions in the water. Similarly,when water flows through the sensing device 10, Pb²⁺ and Hg²⁺ ions inthe water may bind to the first and second receptors, respectively, andsignals (e.g. fluorescence) may be generated from each of the first andsecond sensors, 16 and 18, upon the bindings. A combined signal may beobtained by the detector 20. Analyzing the combined signal may thusindicate the total toxicity of the Pb²⁺ and Hg²⁺ ions in the water.

In yet another embodiment, the sensing device 10 may include more thantwo sensors, for example, four sensors, for the detection of a totaltoxicity of water. In this embodiment, each of the Pb²⁺, Hg²⁺, Cd²⁺, andAs³⁺ ions in water may coordinate to a corresponding sensor of thesensing device 10. Likewise, after the detector gathers a total signalgenerated by each sensor, the total toxicity of the water may thus bedetermined.

FIG. 2 depicts a schematic diagram of a chemosensor 30 configured to beused in the sensing system 10 described in FIG. 1 . As shown in FIG. 2 ,the chemosensor 30 is a receptor/spacer/fluorophore-type sensor.Specifically, the chemosensor 30 may be linked to a tethering matrix viaan anchor 32 thereof. The tethering matrix may include, but not limitedto, cellulose microparticles, cellulose films, polymethyl methacrylate(PMMA), polystyrene (PS) microparticles, polyethlene terephthalate (PET)layers, or silicone. The tethering matrix may have a size in a range of1 to 100 μm and may be embedded within hydrogels. The hydrogels may be,but not limited to, polyurethane or poly(2-hydroxyethyl methacrylate)(Poly-HEMA). In addition, the tethering matrix and the hydrogels may besupported by a polymer support. The polymer support may be, but notlimited to, PET.

Still referring to FIG. 2 , the chemosensor also includes a fluorophore34 bound to the anchor 32, and a spacer 36 bound to the fluorophore 34.The fluorophore 34 may be, but not limited to, anthracene, benzene,carbazole, diphenylfurane, naphthalene, 1,8-naphthalimide,N,N,N′,N′-tetramethylbenzidine, porphyrin, or pyrene. The spacer 36 maybe, but not limited to, methylamine and ethylamine. Further, thechemosensor 30 includes a receptor 38 bound to the spacer 36, where thereceptor 38 may coordinate to analytes (e.g. ions) for analytedetection.

FIG. 3 depicts a schematic diagram of another sensing device accordingto the present disclosure. The sensing device 50 includes an inlet 52,an outlet 54, a sensor film 56, and a detector 58. The detector 58 maybe a photodetector. Further, the sensor film 56 may include a mixture ofsensors embedded therein, where the sensors are mixed by a variablemixing ratio α. The mixing ratio α may be in a range of 0.05 and 0.95.Further, by adjusting the mixing ratio α, a total signal collected bythe detector 58 may depend substantially on a total concentration of thedetected analytes in a fluid medium (e.g. water).

In order for the total signal to depend substantially on the totalconcentration of the detected analytes, the mixing ratio α needs to bedefined when fabricating the sensing device 50. Now, methods fordefining the mixing ratio α are described. As a non-limiting example,the sensors described hereafter is a chemosensor as illustrated in FIG.2 . The methods described hereafter may also be applicable when othertypes of sensors are employed in manufacturing the sensing device 50.

First, a situation where a sensor includes one receptor which can bindto one analyte is described. Suppose that an analyte A may bind to areceptor R in an aqueous solution, forming a chemical entity AR. In theaqueous solution, the concentration of the chemical entity AR, [AR], isin an equilibrium with the concentration of the analyte A, [A], and theconcentration of the receptor R, [R]. A general reaction is depictedbelow as reaction (2):AR⇄A+R  (2)

In addition, the binding strength between the analyte A and the receptorR relates to a dissociation constant K_(d) of the binding, which isdefined as formula (3):K _(d) =c ⁰ e ^(ΔG/k) ^(B) ^(T)  (3)In formula (3), c⁰ is a reference concentration, ΔG is the Gibbs freeenergy of the binding, k_(B) is the Boltzmann constant, and T is anabsolute temperature.

Referring to reaction (2), the dissociation constant K_(d) of thebinding between the analyte A and the receptor R is therefore expressedas stated below as formula (4):

$\begin{matrix}{K_{d} = \frac{\lbrack A\rbrack\lbrack R\rbrack}{\left\lbrack {AR} \right\rbrack}} & (4)\end{matrix}$

Alternatively, formula (4) may be represented as formula (5):

$\begin{matrix}{K_{d} = \frac{\left\lbrack c_{1} \right\rbrack\left\lbrack c_{unb} \right\rbrack}{\left\lbrack c_{b} \right\rbrack}} & (5)\end{matrix}$In formula (5), c₁ is the concentration of the analyte A in the aqueoussolution, c_(unb) is the concentration of the receptor R not bound bythe analyte A, and c_(b) is the concentration of the receptor R bound bythe analyte A.

Further, upon binding, the sensor may generate a signal (e.g.fluorescence). The signal can be given by the following formula (6):

$\begin{matrix}{{signal} = \frac{{s_{1}c_{b}} + {s_{0}c_{unb}}}{c_{b} + c_{unb}}} & (6)\end{matrix}$In formula (6), s₁ is the signal when the receptor R is bound by theanalyte A, and s₀ is the signal when the receptor R is in an unboundstate (i.e. not bound by the analyte A). In one example, s₁=100s₀.

Based on formula (6), the relative signal signal/s₀ can be expressed asstated below:

$\begin{matrix}{\frac{signal}{s_{0}} = \frac{{\frac{s_{1}}{s_{0}}c_{b}} + c_{unb}}{c_{b} + c_{unb}}} & (7)\end{matrix}$

Therefore, according to formula (5), formula (7) can be transformed intothe following formula (8):

$\begin{matrix}{\frac{signal}{s_{0}} = \frac{1 + \frac{c_{1}s_{1}}{K_{d}s_{0}}}{1 + \frac{c_{1}}{K_{d}}}} & (8)\end{matrix}$

FIG. 4 depicts three titration curves of signal/s₀ as a function of theconcentration of the analyte A (c₁) for three different dissociationconstants. As shown in FIG. 4 , for a specific concentration of theanalyte A (c₁), a higher value K_(d) corresponds to a lower relativesignal (signal/s₀) value. Typically, the titration curve measurement ischosen for K_(d) to be close to the concentration of interest.

Next, the situation where a sensor includes one receptor which can bindto two different analytes is described. Suppose that a receptor R iscross-receptive between two different analytes, analyte A₁ and analyteA₂. In this situation, the receptor R may have three different states,(a) an unbound state, (b) bound by analyte A₁, and (c) bound by analyteA₂. Therefore, upon binding, a total signal from the receptor R,following the logic of formula (8), can be expressed as described below:

$\begin{matrix}{{signa{l_{R}/s_{0}}} = \frac{1 + \frac{c_{1}s_{1}}{K_{d}^{A{1_{s}}_{0}}} + \frac{c_{2}s_{2}}{K_{d}^{A2_{s_{0}}}}}{1 + \frac{c_{1}}{K_{d}^{A1}} + \frac{c_{2}}{K_{d}^{A2}}}} & (9)\end{matrix}$In formula (9), c₁ is the concentration of the analyte A₁ in the aqueoussolution, c₂ is the concentration of the analyte A₂ in the aqueoussolution, K_(d) ^(A) ¹ is the dissociation constant of the bindingbetween the receptor R and the analyte A₁, K_(d) ^(A) ² is thedissociation constant of the binding between the receptor R and theanalyst A₂, s₁ is the signal when the receptor R is bound by the analyteA₁, s₂ is the signal when the receptor R is bound by the analyte A₂, ands₀ is the signal when the receptor R is in the unbound state. In oneexample, s₂=s₁=100s₀.

Furthermore, using the logic of formula (9), if the receptor R can bindto multiple analytes (i.e. more than two analytes), a total signal fromthe receptor R due to the binding of the analytes is accordinglyexpressed as described below, where i represents the index over theanalytes:

$\begin{matrix}{{signa{l_{R}/s_{0}}} = \frac{1 + {\sum\limits_{i}\frac{c_{i}s_{i}}{K_{d}^{{Ai}_{s_{0}}}}}}{1 + {\sum\limits_{i}\frac{c_{i}}{K_{d}^{Ai}}}}} & (10)\end{matrix}$

Referring again to FIG. 3 , the sensor film 56 may include a mixture ofsensors in a variable mixing ratio α, and each of the sensors mayinclude a receptor configured to coordinate to an analyte in a fluidmedium. Therefore, upon binding, the total signal of the sensing device50 is the sum of signals from each of the sensors embedded in the sensorfilm 56. Based on formula (10), such a total signal can be given asdescribed below:

$\begin{matrix}{{signal} = {{\sum\limits_{a}{\alpha_{a}*signal_{a}}} = {\sum_{a}{\alpha_{a}*\frac{1 + {\sum\limits_{i}\frac{c_{i}s_{i}}{K_{d}^{{ai}_{s_{0}}}}}}{1 + {\sum\limits_{i}\frac{c_{i}}{K_{d}^{ai}}}}}}}} & (11)\end{matrix}$In formula (11), α represents the number of sensors embedded in thesensor film 56, signal_(α)represents the normalized signal generated byone of the sensors embedded in the sensor film 56, and α_(α)representsthe ratio of the amount of the one of the sensors embedded in the sensorfilm 56 to the total amount of the sensors embedded in the sensor film56.

To obtain an optimal value of α_(α), the absolute gradient of a signalshall be maximized with respect to the quantity of interest andminimized with respect to all conjugate quantities. For example, in anembodiment where a sensing device is used to determine a total hardnessof water, the total hardness of water is substantially proportional to atotal concentration of the Ca²⁺ and Mg²⁺ ions, c_(Cα)+c_(Mg), in thewater. As such, an optimal value of α_(α) may be determined using thefollowing mathematical formulas (12) and (13):

$\begin{matrix}{\arg_{\alpha}\max{❘\frac{d({signal})}{d\left( {c_{Ca} + c_{Mg}} \right)}❘}} & (12)\end{matrix}$ $\begin{matrix}{\arg_{\alpha}\min{❘\frac{d({signal})}{d\left( {c_{Ca} - c_{Mg}} \right)}❘}} & (13)\end{matrix}$

In one embodiment, the sensor film 56 of the sensing device 50 mayinclude a first sensor configured to detect a first analyte (A₁) in afluid medium (e.g. water) and a second sensor configured to detect asecond analyte (A₂) in the fluid medium, where the second analyte (A₂)is different from the first analyte (A₁). The first and second sensorsare mixed in the sensor film 56 by a mixing ratio α. The mixing ratio αmay be in a range of 0.05 and 0.95.

Specifically, the first sensor may be a chemosensor with a firstreceptor configured to selectively coordinate to the first analyte (A₁).Upon coordination by the first analyte (A₁), the first sensor maygenerate a first signal (e.g. fluorescence). In addition, the secondsensor may be a chemosensor with a second receptor configured toselectively coordinate to the second analyte (A₂). Upon coordination bythe second analyte (A₂), the second sensor may generate a second signal(e.g. fluorescence). The detector may combine the first and secondsignals to provide a total signal. According to formula (14), the totalsignal can be expressed as stated below:

$\begin{matrix}{{signal} = {\frac{1 + \frac{c_{1}s_{1}}{K_{d}^{A_{1}s_{0}}}}{1 + \frac{c_{1}}{K_{d}^{A_{1}}}} + {\alpha\frac{1 + \frac{c_{2}s_{2}}{K_{d}^{A_{2}s_{0}}}}{1 + \frac{c_{2}}{K_{d}^{A_{2}}}}}}} & (14)\end{matrix}$In formula (14), c₁ is the concentration of the analyte A₁ in the fluidmedium, c₂ is the concentration of the analyte A₂ in the fluid medium,K_(d) ^(A) ¹ is the dissociation constant of the binding between thefirst receptor and the first analyte A₁, K_(d) ^(A) ² is thedissociation constant of the binding between the second receptor and thesecond analyte A₂, s₁ is the signal when the first receptor is bound bythe first analyte A₁, s₂ is the signal when the second receptor is boundby the second analyte A₂, and s₀ is the signal when the first and secondreceptors are not bound by the first and second analytes, A₁ and A₂. Inone example, s₂=s₁=100 s₀.

When applying the sensing device 50 to the determination of a totalhardness of water, the first sensor may be a chemosensor with a firstreceptor configured to coordinate to Ca²⁺ ions in the water, and thesecond sensor may be a chemosensor with a second receptor configured tocoordinate to Mg²⁺ ions in the water. To make the total signal dependsubstantially on a total concentration of the Ca²⁺ and Mg²⁺ ions in thewater, a mixing ratio α of the first and second sensors may bedetermined, using formula (12) and (13), when fabricating the sensorfilm 56. Suppose the water is rich in Ca²⁺ ions and that the totalhardness (dGH) of a sample water is around 5. Further, in formula (14),suppose s₂=s₁=100s₀, and that the dissociation constants for the firstand second sensors, K_(d) ^(A) ¹ and K_(d) ^(A) ² , are both 1 mM. Usingformulas (12) and (13), an optimal mixing ratio α=0.65 may therefore becalculated. With the mixing ratio α=0.65, the total signal of thesensing device 50 may be substantially proportional to the totalconcentration of the Ca²⁺ and Mg²⁺ ions in the water. The total signalmay not be affected substantially by the individual concentration of theCa²⁺ or Mg²⁺ ions in the water so long as the total concentration of theCa²⁺ and Mg²⁺ ions in the water remains substantially the same.

FIG. 5 depicts titration curves of signal/s₀ as a function of the totalhardness of water (dGH), when s₂=s₁=100 s₀, and the dissociationconstants for the first and second sensors, K_(d) ^(A) ¹ and K_(d) ^(A)² , are both 1 mM. In FIG. 5 , the titration curves represent situationswhere a total concentration of the Ca²⁺ and Mg²⁺ ions in the water aresubstantially the same. However, each of the titration curvescorresponds to a different fraction of the individual concentration ofCa²⁺ ions to the individual concentration of Mg²⁺ ions in the water. Thetitration curve W corresponds to a situation where the fraction of theindividual concentration of Ca²⁺ ions to the individual concentration ofMg²⁺ ions in the water is 0.5. The titration curve X corresponds to asituation where the fraction of the individual concentration of Ca²⁺ions to the individual concentration of Mg²⁺ ions in the water is 1. Thetitration curve Y corresponds to a situation where the fraction of theindividual concentration of Ca²⁺ ions to the individual concentration ofMg²⁺ ions in the water is 2. The titration curve Z corresponds to asituation where the fraction of the individual concentration of Ca²⁺ions to the individual concentration of Mg²⁺ ions in the water is 6.

Referring to FIG. 5 , although the fractions of the individualconcentration of Ca²⁺ ions to the individual concentration of Mg²⁺ ionsof each titration curve are different, a specific relevant signal(signal/s₀) value, however, may correspond to a dGH with minimaldeviations (e.g. around 5%). For example, if the sensing devicedetermines a relevant signal (signal/s₀) value of 60, the sensing devicemay then provide the total hardness of water (dGH) as 6 (or closelyaround 6). Similarly, if the sensing device determines a relevant signal(signal/s₀) value of 40, the sensing device may then indicate the totalhardness of water (dGH) as 3.5 (or closely around 3.5).

The sensing device 50 described in FIG. 3 may also be employed toanalyze a total toxicity of water. As mentioned above, the totaltoxicity of water may be due to the presence of heavy metal ions, suchas Pb²⁺, Hg²⁺, Cd²⁺, As³⁺, or As⁵⁺ ions. Therefore, in this embodiment,the sensor film 56 of the sensing device 50 may include a first sensorand a second sensor, where the first and second sensors are embedded inthe sensor film 56 by a mixing ratio α. Specifically, the first sensormay be a chemosensor with a first receptor configured to coordinate toPb²⁺ ions in the water, and the second sensor may be a chemosensor witha second receptor configured to coordinate to Hg²⁺ ions in the water. Tomake the total signal depend substantially on a total concentration ofthe Pb²⁺ and Hg²⁺ ions, an optimal mixing ratio α may be defined, usingthe formulas (12) and (13), when fabricating the sensor film 56. Withthe optimal mixing ratio α, the total signal provided by the sensingdevice 50 is substantially proportional to the total toxicity of thewater. Therefore, the total toxicity of the water may be determinedbased on the total signal.

Moreover, if the sensing device 50 includes more than two sensors, forexample, four sensors, embedded in the sensor film 56 by a mixing ratioα, each of the Pb²⁺, Hg²⁺, Cd²⁺, and As³⁺ ions may coordinate to acorresponding sensor in the sensor film 56. Likewise, because the totalsignal obtained from all the four sensors depends substantially on atotal concentration of the Pb²⁺, Hg²⁺, Cd²⁺, and As³⁺ ions in the water,the total toxicity of the water may therefore be determined based on thetotal signal.

Apart from a sensing device having one detector that collects signals ofdifferent frequency values, the sensing device may include more than onedetector such that each detector may collect signals of correspondingfrequency values. FIG. 6 depicts a schematic diagram of yet anothersensing device according to the present disclosure. Specifically, thesensing device 70 includes an inlet 72, an outlet 74, a sensor film 76,a first detector 78, and a second detector 80. The first and seconddetectors, 78 and 80, may be photodetectors. Further, the sensor film 76may include a mixture of sensors embedded therein, where the sensors aremixed by a variable mixing ratio α. The mixing ratio α may be in a rangeof 0.05 and 0.95.

In one embodiment, the sensing device 70 may be used to simultaneouslydetermine a total hardness of water and a total toxicity of the water.Referring to FIG. 6 , the sensor film 76 may include a first sensor anda second sensor, where the first and second sensors are mixed in thesensor film 76 by a mixing ratio α. Specifically, the first sensor maybe a chemosensor with a first receptor configured to coordinate to Ca²⁺ions in the water. Upon binding by the Ca²⁺ ions, the first sensor maygenerate a first signal (e.g. fluorescence) with a first frequency. Inthis embodiment, the first signal may be collected by the first detector78, where the total hardness of water may be determined based on thefirst signal. Similarly, the second sensor may be a chemosensor with asecond receptor configured to coordinate to Pb²⁺ ions in the water. Uponbinding by the Pb²⁺ ions, the second sensor may generate a second signal(e.g. fluorescence) with a second frequency. Accordingly, the secondsignal may be received by the second detector 80, where the totaltoxicity of the water may be calculated based on the second signal.

To better achieve this purpose, a first filter 82 may be positionedbetween the sensor film 76 and the first detector 78. The first filter82 is configured to filter out the second signal. In addition, a secondfilter 84 may be positioned between the sensor film 76 and the seconddetector 80. Similarly, the second filter 84 is configured to filter outthe first signal.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms encompassed by the claims.The words used in the specification are words of description rather thanlimitation, and it is understood that various changes can be madewithout departing from the spirit and scope of the disclosure. Aspreviously described, the features of various embodiments can becombined to form further embodiments of the present disclosure that maynot be explicitly described or illustrated. While various embodimentscould have been described as providing advantages or being preferredover other embodiments or prior art implementations with respect to oneor more desired characteristics, those of ordinary skill in the artrecognize that one or more features or characteristics can becompromised to achieve desired overall system attributes, which dependon the specific application and implementation. These attributes caninclude, but are not limited to cost, strength, durability, life cyclecost, marketability, appearance, packaging, size, serviceability,weight, manufacturability, ease of assembly, etc. As such, to the extentany embodiments are described as less desirable than other embodimentsor prior art implementations with respect to one or morecharacteristics, these embodiments are not outside the scope of thedisclosure and can be desirable for particular applications.

What is claimed is:
 1. A sensing device comprising: a first sensor having a first receptor capturing a first analyte (A₁) in a fluid medium at a c₁ concentration generating a first signal s₁ when the first receptor is bound by the first analyte; a second sensor having a second receptor capturing a second analyte (A₂) in the fluid medium at a c₂ concentration generating a second signal s₂ when the second receptor is bound by the second analyte, the second analyte being different from the first analyte, the first and second sensors present to each other in a mixing ratio (α); and a detector comprising a processor programmed to perform the step of solving for the mixing ratio (α) using the following equations: ${{signal} = {\frac{1 + \frac{c_{1}s_{1}}{K_{d}^{A1_{{s}_{0}}}}}{1 + \frac{c_{1}}{K_{d}^{A1}}} + {\alpha\frac{1 + \frac{c_{2}s_{2}}{K_{d}^{A2_{s_{0}}}}}{1 + \frac{c_{2}}{K_{d}^{A2}}}}}},$ ${\arg_{\alpha}\max{❘\frac{d({signal})}{d\left( {c_{1} + c_{2}} \right)}❘}},{{and}\arg_{\alpha}\min{❘\frac{d({signal})}{d\left( {c_{1} - c_{2}} \right)}❘}}$ where K_(d) ^(A) ¹ is a dissociation constant of the binding between the first receptor and the first analyte A₁, K_(d) ^(A) ² is a dissociation constant of the binding between the second receptor and the second analyte A₂, s₀ is the signal when the first and second receptors are not bound by the first and second analytes, A₁ and A₂, respectively; and the processor of the detector further programmed to collect the first signal s₁ and the second signal s₂ to calculate a total signal and a total concentration of the first analyte (A₁) and the second analyte (A₂) in the fluid based on the total signal and the mixing ratio (α).
 2. The sensing device of claim 1 further comprising a first spacer, a first fluorophore, and a first anchor, the first spacer is bound to the first receptor, the first fluorophore is bound to the first spacer, and the first anchor is bound to the first fluorophore.
 3. The sensing device of claim 2, wherein the first fluorophore is selected from the group consisting of anthracene, benzene, carbazole, diphenylfurane, naphthalene, 1,8-naphthalimide, N,N,N′,N′-tetramethylbenzidine, porphyrin, and pyrene.
 4. The sensing device of claim 2, wherein the first sensor is linked to a tethering matrix via the first anchor, the tethering matrix embedded with hydrogels.
 5. The sensing device of claim 4, wherein the hydrogels are polyurethane or poly(2-hydroxyethyl methacrylate) (Poly-HEMA).
 6. The sensing device of claim 1 further comprising a second spacer, a second fluorophore, and a second anchor, the second spacer is bound to the second receptor, the second fluorophore is bound to the second spacer, and the second anchor is bound to the second fluorophore.
 7. The sensing device of claim 6, wherein the second fluorophore is selected from the group consisting of anthracene, benzene, carbazole, diphenylfurane, naphthalene, 1,8-naphthalimide, N,N,N′,N′-tetramethylbenzidine, porphyrin, and pyrene.
 8. The sensing device of claim 6, wherein the second sensor is linked to a tethering matrix via the second anchor, the tethering matrix embedded with hydrogels.
 9. The sensing device of claim 8, wherein the hydrogels are polyurethane or poly(2-hydroxyethyl methacrylate) (Poly-HEMA).
 10. A sensing device comprising: a sensor film having a mixture of sensors, the mixture of sensors including first and second sensors, the first and second sensors present to each other in a mixing ratio (α), the first sensor having a first receptor capturing a first analyte (A₁) in a fluid medium at a c₁ concentration generating a first signal s₁ when the first receptor is bound by the first analyte and the second sensor having a second receptor capturing a second analyte (A₂) in the fluid medium at a c₂ concentration generating a second signal s₂ when the second receptor is bound by the second analyte, the sensor film generating a signal in response to the first sensor capturing the first analyte and the second sensor capturing the second analyte; and a detector comprising a processor programmed to perform the step of solving for the mixing ratio (α) is solved using the following equations: ${{signal} = {\frac{1 + \frac{c_{1}s_{1}}{K_{d}^{A1_{{s}_{0}}}}}{1 + \frac{c_{1}}{K_{d}^{A1}}} + {\alpha\frac{1 + \frac{c_{2}s_{2}}{K_{d}^{A2_{s_{0}}}}}{1 + \frac{c_{2}}{K_{d}^{A2}}}}}},$ ${\arg_{\alpha}\max{❘\frac{d({signal})}{d\left( {c_{1} + c_{2}} \right)}❘}},{{and}\arg_{\alpha}\min{❘\frac{d({signal})}{d\left( {c_{1} - c_{2}} \right)}❘}}$ where K_(d) ^(A) ¹ is a dissociation constant of the binding between the first receptor and the first analyte A₁, K_(d) ^(A) ² is a dissociation constant of the binding between the second receptor and the second analyte A₂, s₀ is the signal when the first and second receptors are not bound by the first and second analytes, A₁ and A₂, respectively; and the processor of the detector further programmed to collect the first signal s₁ and the second signal s₂ to calculate a total signal and a total concentration of the first analyte (A₁) and the second analyte (A₂) in the fluid based on the total signal and the mixing ratio (α).
 11. The sensing device of claim 10 further comprising a first spacer, a first fluorophore, and a first anchor, the first spacer is bound to the first receptor, the first fluorophore is bound to the spacer, and the first anchor is bound to the first fluorophore.
 12. The sensing device of claim 11, wherein the fluorophore is selected from the group consisting of anthracene, benzene, carbazole, diphenylfurane, naphthalene, 1,8-naphthalimide, N,N,N′,N′-tetramethylbenzidine, porphyrin, and pyrene.
 13. A sensing device comprising: a sensor film having a mixture of sensors, the mixture of sensors including first and second sensors, the first and second sensors present to each other in a mixing ratio (α), the first sensor having a first receptor capturing a first metal ion analyte (A₁) in a fluid medium at a c₁ concentration generating a first signal s₁ when the first receptor is bound by the first metal ion analyte and the second sensor having a second receptor capturing a second metal ion analyte of (A₂) in the fluid medium at a c₂ concentration generating a second signal s₂ when the second receptor is bound by the second metal ion analyte, the mixing ratio depending on the first and second metal ion analytes, the sensor film generating a signal in response to the first sensor capturing the first metal ion analyte and the second sensor capturing the second metal ion analyte; and a detector comprising a processor programmed to perform the step of solving for the mixing ratio (α) using the following equations: ${{signal} = {\frac{1 + \frac{c_{1}s_{1}}{K_{d}^{A1_{{s}_{0}}}}}{1 + \frac{c_{1}}{K_{d}^{A1}}} + {\alpha\frac{1 + \frac{c_{2}s_{2}}{K_{d}^{A2_{s_{0}}}}}{1 + \frac{c_{2}}{K_{d}^{A2}}}}}},$ ${\arg_{\alpha}\max{❘\frac{d({signal})}{d\left( {c_{1} + c_{2}} \right)}❘}},{{and}\arg_{\alpha}\min{❘\frac{d({signal})}{d\left( {c_{1} - c_{2}} \right)}❘}}$ where K_(d) ^(A) ¹ is a dissociation constant of the binding between the first receptor and the first metal ion analyte A₁, K_(d) ^(A) ² is a dissociation constant of the binding between the second receptor and the second metal ion analyte A₂, s₀ is the signal when the first and second receptors are not bound by the first and second metal ion analytes, A₁ and A₂, respectively; and the processor of the detector further programmed to calculate a total concentration of the first metal ion analyte (A₁) and the second metal ion analyte (A₂ ) in the fluid medium based on a total signal of first signal s₁ and the second signal s₂ and the mixing ratio (α).
 14. The sensing device of claim 13, further comprising a first spacer, a first fluorophore, and a first anchor, the first spacer is bound to the first receptor, the first fluorophore is bound to the first spacer, and the first anchor is bound to the first fluorophore.
 15. The sensing device of claim 14, wherein the first fluorophore is selected from the group consisting of anthracene, benzene, carbazole, diphenylfurane, naphthalene, 1,8-naphthalimide, N,N,N′,N′-tetramethylbenzidine, porphyrin, and pyrene.
 16. The sensing device of claim 14, wherein the first sensor is linked to a tethering matrix via the first anchor, the tethering matrix embedded with hydrogels.
 17. The sensing device of claim 16, wherein the hydrogels are polyurethane or poly(2-hydroxyethyl methacrylate) (Poly-HEMA).
 18. The sensing device of claim 13 further comprising a second spacer, a second fluorophore, and a second anchor, the second spacer is bound to the second receptor, the second fluorophore is bound to the second spacer, and the second anchor is bound to the second fluorophore.
 19. The sensing device of claim 13, wherein the first and second receptors are the same receptor.
 20. The sensing device of claim 13, wherein the first metal ion analyte is Ca²⁺ ions and the second metal ion analyte is Mg²⁺ ions. 